1. Field of the Invention
The present invention relates to a vehicle steering apparatus for holding a pad portion disposed at a substantially central portion of a steering wheel in a non-rotatable state when the steering wheel is rotated.
2. Description of the Related Art
One arrangement of a vehicle steering apparatus with a non-rotatable pad portion is shown in FIG. 1 of Published Unexamined Japanese Utility Model Application No. 53-105234. In this prior art, a pad portion disposed at a substantially central portion of a steering wheel is provided to a stationary shaft fixed to a vehicle body side. The steering wheel is rotatably mounted on the stationary shaft. In addition, a steering shaft is coupled to a steering gear mechanism to be separated from the steering wheel. Furthermore, a gear provided on a boss portion of the steering wheel is externally meshed with a gear provided on the steering shaft side. Thus, a two-shaft external gear meshing type structure for transmitting rotation of the steering wheel to the steering gear mechanism via a meshing mechanism of these gears upon rotation of the steering wheel is adopted.
Another prior art example is a vehicle steering apparatus shown in FIG. 2 of Published Unexamined Japanese Utility Model Application No. 53-105234 is known. In this prior art, a pad portion disposed at a substantially central portion of a steering wheel is attached to a stationary shaft fixed to a vehicle body side. Furthermore, the steering wheel is rotatably supported on the end portion of a hollow steering shaft disposed on the outer surface of the stationary shaft. The outer surface of the steering shaft is rotatably supported by a steering column, so that rotation of the steering wheel is directly transmitted to the steering shaft. However, in the former two-shaft external gear meshing type mechanism, the gear provided on the boss portion of the steering wheel and the gear arranged o the steering wheel shaft are externally meshed, and rotation of the steering wheel is transmitted to the steering gear mechanism via the meshing mechanism of these gears. Therefore, the rotational direction of the steering wheel is opposite to that of the sheering shaft, and a meshing reversal mechanism must be arranged in the meshing mechanism of the gear of the steering wheel shaft and the gear of the steering shaft. For this reason, the structure of a transmission mechanism for transmitting the rotation of the steering wheel to the steering gear mechanism side is complicated, resulting in an increase in cost. Furthermore, since the gear of the steering wheel is externally meshed with the gear of the steering shaft, the pressure angle of teeth is large. Thus, when a simple spur gear is used, noise such as meshing noise is easily generated.
In the latter structure, a fixing portion of the stationary shaft to the vehicle body must be arranged in front of the steering gear mechanism at the front end of the steering shaft. Therefore, the structure for arranging the fixing portion is complicated. Furthermore, when switches are arranged on the pad portion at substantially the central portion of the steering wheel, harness for these switches is guided outside the passenger compartment through the interior of the stationary shaft. Thus, the protection and assembly of wirings of the harnesses around the stationary shaft are cumbersome.